The human brain holds around 86 billion neurons, wired together in a vast web of hundreds of trillions of connections. These connections, bridged by structures called synapses, form circuits responsible for everything we feel, perceive and do. And they constantly shift as we grow, learn, make memories and form habits.
Neuroscientists have long sought to hack into these circuits to understand how the brain works. Just 20 years ago they developed a technique called optogenetics, which offered some of the first glimpses of these circuits in action—it uses light to turn cells, including brain cells, on and off.
The work won three scientists the 2026 Nobel Prize in Physiology or Medicine. If brain pathways were highways, optogenetics would be akin to “controlling the volume of traffic on a road network that’s already built,” says Sangkyu Lee, a neurobiologist at the Institute for Basic Science in South Korea.
Better yet, however, would be “changing the structure of the ‘road’ itself,” Lee says—by actually editing the brain’s connections. More recently, scientists have figured out how to add new connections and delete existing ones, and they have used these techniques to change animals’ behavior and even to implant memories. Ultimately, these tools could yield discoveries about the brain and potentially even treatments for psychiatric conditions such as post-traumatic stress disorder (PTSD), schizophrenia and obsessive-compulsive disorder (OCD).
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